The present invention relates generally to electrical signal processing techniques utilized with an ultrasonic exploratory system and, more particularly, to signal analyzing in fetal monitoring.
In ultrasonic exploratory scanning, physiological data is derived from a patient, for monitoring and/or therapeutic purposes, by transmitting ultrasonic energy into the patient's body and then collecting and processing the data derived, in the form of an intelligence, for diagnostic purposes. However, problems are often encountered in analyzing such data due to the signals derived from the multiple sounds and associated noise collected from the body site being investigated.
In particular, in the field of fetal monitoring, the frequent movement of the fetus adds to the problem of deriving reliable signals indicative of fetal heart rate. The problem is intensified even more as a consequence of the multiple sounds generated by the front and rear wall of the heart, heart valves, etc., in addition to the nonsynchronous impulse noise caused by the fetal and mother movements. Naturally, processing of multiple signals with background noise within a single heartbeat, if processed as consecutive heartbeat signals, would produce a false indication of the fetal heart rate, and therefore provide unreliable instrumentation. Long term averaging techniques are not permissable since it is important that rapid changes in fetal heart rate be observed.
One improvement made to help obviate such problems is disclosed in U.S. Pat. Application Ser. No. 205,942, now U.S. Pat. No. 3,763,851 filed Dec. 8, 1971 by Haff and Hatke for a Fetal Monitoring Technique. The latter improvement discloses ultrasonic apparatus for monitoring heartbeat activity from Doppler shifted information derived from heartbeat motion. The Doppler shifted information is fed to an adjustable resonant circuit for de-emphasizing Doppler signal frequency content other than that about the resonant circuit frequency, and comparing input signals to, and output signals from the resonant circuit for detecing a phase difference, if any, which is employed for adjusting the frequency of the resonant circuit at a preselected rate. Such a technique provides a phase locked tracking filter which helps to suppress and eliminate undesired signals.
Despite the achievement of displaying reliable fetal heart rates with the technique disclosed in the above-referenced application, it was found that a still more reliable fetal heart rate count from the Doppler signal could be attained to provide an automatic operating system to handle the quick transition from tachycardia to bradycardia conditions which is highly desirable for monitoring fetal heart rates.